Silicon carbide (SiC) is a thermally and chemically stable compound semiconductor. Compared with silicon (Si), SiC has an excellent bandgap, breakdown voltage, electron saturation velocity, and thermal conductivity. Therefore, SiC has gained attention as the next generation power device material.
SiC is well known as a substance having a crystal polymorphism. A typical crystal polymorphism of SiC includes a 6H type (hexagonal system having 6 molecules per cycle), a 4H type (hexagonal system having 4 molecules per cycle), and a 3C type (cubic system having 3 molecules per cycle). SiC to be used for power device material is preferably a single crystal made up of one crystal polymorphism, and the SiC single crystal preferably has less crystal defects.
In particular, for vertical type power devices such as an SBD (Shottky Barrier Diode) and a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), an n-type SiC single crystal having lower electric resistance is preferably applied. Upon manufacturing an n-type SiC single crystal, it is preferable that there is less variation in the dopant concentration among individuals of a plurality of SiC single crystals manufactured. That is, it is preferable that there is not much difference in the dopant concentration among a plurality of SiC single crystal ingots manufactured. In other words, among a plurality of SiC single crystals manufactured, it is preferable that not much difference occurs between the dopant concentration of one SiC single crystal ingot and that of another SiC single crystal ingot.
By the way, the method for manufacturing a SiC single crystal includes a sublimation method and a liquid phase growth method. A method for manufacturing a SiC single crystal by the sublimation method is disclosed, for example, in JP05-262599A (Patent Document 1). Moreover, a method for manufacturing a SiC single crystal by the liquid phase growth method is disclosed in, for example, JP2004-2173A (Patent Document 2).
The liquid phase growth method is more likely to provide a single crystal having less crystal defects compared to the sublimation method. A top seeded solution growth method (hereinafter referred to as a TSSG method), which is one of the liquid phase growth methods, immerses a SiC seed crystal made up of a SiC single crystal into a SiC solution housed in a crucible. Next, the TSSG method grows a SiC single crystal on the SiC seed crystal while pulling up the SiC seed crystal.
The TSSG method grows a SiC single crystal while pulling up a SiC seed crystal. Therefore, it is possible to obtain a long-size SiC single crystal. As described above, since the TSSG method grows the SiC single crystal while pulling up the SiC seed crystal, it resembles to the Czochralski (CZ) process. On that account, the diameter expanding technique of Si single crystal in the CZ process can be transferred to the TSSG. On that account, the TSSG method is suitable for the manufacturing of a large diameter, long-size SiC single crystal ingot having few crystal defects.